X-ray apparatus



Patented Mar. 15, 1938 UNITED STATES X-RAY APPARATUS Alfred Ungelenk, Thuringen, Germany, assignor to General Electric Company, a. corporation of New York Application November 20, 1929, SerialiNo. 408,587

In Germany December 8, 1928 3 Claims.

The present invention relates to X.-ray apparatus and more particularly to tubes which are designed to yield a large X-ray output Without overheating and Without melting the metal on the surface of the electrode subjected to the impact of discharge.

In X-ray and other devices which employ relatively high voltages, hence exceedingly fast moving electron streams in order to obtain a desired output, the impact with which the stream strikes the metal target or anode gives rise to considerable heat which may melt and volatilize the metal of the target. Various expedients have been proposed to reduce this heating effect and many of them have for their object the successive presentation of fresh portions of the anode surface to the ray stream thereby precluding the concentration of heat in a restricted region.

While tubes in which the various features have been incorporated operate fairly satisfactorily, still there are certain objections attending their use. It has been proposed to change the position of the focus on the target by means of a continuous relative movement between the cathode and anode during operation, the movement being obtained specifically by rotating the anode which is mounted in bearings and maintaining the envelope and the cathode fixed in space. It has been found in this case that the heat generated at the target can be dissipated only comparatively inefliciently due to the relatively poor contact between the various parts communicating with the exterior. It has also been proposed to rotate about its axis an X-ray tube in which both electrodes are fixed and correspondingly to change or deflect the path of the cathode rays by electromagnetic action thereby to cause a corresponding movement of the spot about the target. This method of causing the spot to fall successively on different portions of the anode has many advantages but is open to the distinct objection that the electromagnetic field may affect adversely the direction of the electron stream and cause a variation or diminution of the quantity of X-rays.

An object of the present invention is to procured to the envelope and the cathode is rotatably mounted. In operation, the envelope and anode are rotated and the cathode structure is maintained fixed by appropriate means. It will be evident that in having a fixed relation between the .anode and the envelope, the metal member which supports the anode or target may be integral with the shank which extends through the envelope to the exterior and hence there is offered an uninterrupted path over which the generated heat may pass freely to the exterior. The means for maintaining the cathode in a fixed position is preferably magnetic but, as will be apparent from perusing the following description when referred to the accompanying drawing, the magnetic field is removed from the region of the cathode rays and hence cannot deflect or otherwise affect adversely the production of X-rays.

In the drawing, Fig. 1 represents an elevational View of the X-ray apparatus improved in accordance with my invention and including the tube, accessories, and associated circuits, while Fig. 2'is a plan view of the cathode structure per se.

Referring to the drawing, numeral I designates an evacuated envelope or tube which terminates in reentrant stems 2 and 3, the latter being shown partly in cross section. Within the envelope, there is an anode 4 faced with a member 5 of highly refractory metal and a cooperating cathode structure 6. The anode is secured to a shank I which is sealed in the reentrant stem 2 and extended to the exterior of the envelope to constitute a shaft 8. A pulley 9 is fixedly mounted on the shaft and a power driven belt II] is passed over the pulley. The shaft is rotatably mounted in a bearing H which may be supported from a base I2. At the other end of the envelope there is a drawn downportion 13 which fits into a counter-bored metal member 14 provided with a pair of rings E5, Iii insulatingly mounted thereon. The member 14 is free to rotate within a bearing it which is also supported from the base l2.

The cathode arrangement 6 comprises a source of electrons H which may take the form of a helical filament or a crimped ribbon presented edgewise to the anode, as shown more clearly in Fig. 2. About the electron source there is arranged a focusing cup 18 of a shape to accommodate the elongated cathode and provided with sloping sides. The cup I8 is arranged preferably to focus the cathode rays over a restricted area on the anode remote from the place where the axis of rotation of the tube intercepts the anode. One end of the filament is connected to the focusing cup and the other end is connected to a rod l8 which passes through an insulating member l9 and is formed into a slip ring 20. The ring fits rotatably over a metallic rod 2| which is held in an upright position, as shown, by a collar 22 of insulation material within a metal sleeve 23. The latter fits snugly within a cylinder 24 also of metal which tightly embraces the reentrant stem 3. The end of the filament remote from the slip ring 20 is joined by a stiff wire 25 to a rod 26 while the rod I8 at the other end of the filament is attached directly to a rod 26 similar to the other rod 26 by an extension member 21. These rods extend for a considerable distance downwardly and terminate in a member 28 of magnetic material and of relatively large metal content. There is a metallic slip ring 29 which is free to rotate about the sleeve 23 and is secured to one of the rods 26 by a horizontal wire 36 or in any other suitable manner. Located exterior to the envelope and in a position directly opposite the metal members 28 there is a plurality of electromagnets 3|, 3| which may be energized by coils 32, 32, connected to a source 33 of direct current. The cathode I1 is energized preferably by alternating current which may be obtained from a transformer 34 connected to brushes 35, 35 which contact with the rings I5, I5. As shown, one ring is electrically connected to the upright rod 2| thereby to one side of the filament, while the other ring is connected to the cylinder 24 thus to the other side of the filament through the sleeve 23, slip ring 29, horizontal wire 30 and the vertical wire 25 to the filament.

The high potential voltage to be applied between the anode and cathode may be obtained from a voltage step-up transformer 36, one end of which may be connected to the secondary of the filament transformer and the other end to a brush 31 which contacts with a slip ring 38. The ring 38 preferably constitutes a part of a cap 39 which fits tightly over the upper end of the tube and contacts with the shaft 8.

When power is applied to the belt ID, the tube, including the anode, rotates, and it is apparent that the electromagnets 3| may be arranged to exert a magnetic pull or attraction on the metallic members 28 thereby to maintain the cathode stationary. The movement between the rotary and stationary parts takes place at the rings 20 and 29. Inasmuch as the cathode I is focused on a portion of the anode off-set from the center of rotation, it is clear that the relative movement between the cathode and anode serves in eifect to move the focal spot over a wide area on the anode, thereby to present a fresh anode surface to the impinging cathode rays. In this manner the heating effects of the rays are distributed over an area greater than the focal spot on the electron receiving surface and the energy capacity of the tube, and hence also the X-ray output,

is correspondingly increased. Moreover, it will be noted that inasmuch as the anode is mounted rigidly within the envelope, there is no necessity for providing a rotating surface between the anode and envelope as in the prior art tubes and consequently the heat generated at the surface of the anode is allowed a ready path through substantial portions of metal to the exterior. If desired, a circular radiator 4|] may be employed to aid in dissipating the heat.

While I have explained and illustrated my invention in connection with an envelope and anode which rotate and with a cathode which is maintained stationary, it will be understood that if desired, the reverse operation may take place in order to obtain a relative movement between the electrodes, i. e., the magnets 3| may be arranged to rotate in any well known manner and to exercise a rotating force on the members 28 while the tube, including the anode secured thereto, may be held stationary.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In X-ray apparatus, the combination of an X-ray tube containing a source of electrons and an electron receiving member, said source being rotatably mounted within the tube, said member being secured to the tube, means for rotating the tube and the said member, and magnetic means cooperating with said source of electrons for maintaining the source stationary whereby a relative movement is obtained between the source of electrons and the anode thereby to increase the X-ray output of the apparatus.

2. In X-ray apparatus, the combination of an X-ray tube containing a source of electrons and an electron receiving member, said source being rotatably mounted within the tube, said member being secured to the tube, means for rotating the tube and the said member, and means cooperating with said source of electrons for maintaining the source stationary whereby a relative movement is obtained between the source of electrons and the anode thereby to increase the X-ray output of the apparatus, said means for maintaining the source of electrons stationary comprising a magnet positioned exterior to the tube.

3. In combination, an X-ray tube comprising an envelope containing an anode fixedly secured to said envelope, a cathode structure including an electron-emitting element, said envelope also containing a bearing member fixedly secured thereto and extending along the axis thereof, said cathode structure being mounted to rotate on said bearing member, said electron-emitting element being positioned remote from said bearing, means for rotating the envelope and the anode as a unit, and means cooperating with said cathode structure for holding fixed in space the cathode beam thereby to focus the beam on the anode at a position removed from the center of rotation of said anode.

ALFRED UNGELENK. 

